1. Technical Field
The present invention relates to an image processing device for detecting a particular pattern included in an original document image read from an original document such as a bank note, a marketable security or a classified document, and to an image forming device provided with the image processing device.
2. Description of Related Art
In recent years, a demand for an image processing device and an image forming device, which can inhibit copying of a copy-inhibited document such as a bank note or a marketable security, for example, and prevent forgery, is growing with the progress of the technique for forming a copy of an original document image. Moreover, a high emphasis is placed on enhancing security by preventing copying of an important document such as a classified document and information leak.
Conventionally, a variety of techniques for judging whether an image of a particular pattern is included in an original document image read from an original document formed on a sheet or not and stopping the formation of an image or forming an image different from the read original document image when it is judged that the image of a particular pattern is included, for example, have been proposed as techniques related to prevention of copying of such an original document image (see Japanese Utility Model Application Laid-Open No. H5-85158, Japanese Patent Application Laid-Open No. 116-178098, Japanese Patent Application Laid-Open No. 2003-99788 and Japanese Patent Application Laid-Open No. 2005-142918). For example, an image processing device provided with a function of detecting a circular image such as a bank note red seal included in an original document image is disclosed in Japanese Utility Model Application Laid-Open No. H5-85158 and Japanese Patent Application Laid-Open No. H6-178098.
An image processing device described in Japanese Utility Model Application Laid-Open No. H5-85158 first performs a thinning process for an image composed of a plurality of red pixels when detecting a red pixel in the main scanning direction in a read original document image. Then, when detecting another red pixel at a particular distance in the main scanning direction from the position of the image processed by the thinning process, the image processing device assumes that the red pixel detected first and the red pixel detected next correspond to both end positions of a segment to be the diameter of a circle and rotates the segment at a predetermined angle relative to the main scanning direction. When the positions of the two pixels at both end positions of the segment exist within a predetermined range of a position of a pixel stored in a memory, the image processing device judges that the red pixels are a circular image having a circular outline.
Moreover, an image processing device described in Japanese Patent Application Laid-Open No. H6-178098 judges that a detected pixel is a part of an image to be detected when pixels corresponding to both ends of a segment to be the diameter of a circle in the main scanning direction are detected from an original document image and a part of the circle is detected at a predetermined distance in the sub scanning direction from the center of the circle. Moreover, said image processing device counts the number of times a pixel within a predetermined interval inside a detected circle becomes on, i.e., the number of red pixels, checks whether a numerical value corresponding to particular image data prestored in a memory accords with the count value or not, and judges that an image formed of a detected pixel is a particular circular image when the numerical value accords.
Furthermore, an image processing device described in Japanese Patent Application Laid-Open No. 2003-99788 judges whether an original document image to be processed includes a particular image part, which is a part of a target image, or not and checks whether a target image candidate including the particular image part is a target image or not, so as to extract a target image in an original document image at high speed and with a high degree of accuracy.
Furthermore, an image processing device described in Japanese Patent Application Laid-Open No. 2005-142918 compares a dot pattern included in image data of an original document image with a stored particular dot pattern, and inhibits output of image data of an original document image so as to prevent unauthorized flow of information when it is judged that the dot patterns are identical.
By the way, when a part of an original document image is enlarged by an image processing device described in Japanese Utility Model Application Laid-Open No. H5-85158, Japanese Patent Application Laid-Open No. H6-178098, Japanese Patent Application Laid-Open No. 2003-99788 or Japanese Patent Application Laid-Open No. 2005-142918, an area, for which whether a particular pattern is included or not is judged, is limited to an area to be enlarged, which is a part of the original document image. For example, when copying for enlarging at 400% is to be performed, whether a particular pattern is included or not is judged only for an area, which is to be enlarged, having a size of 1/16 of the entire original document image.